Infrared focal plane arrays operating in the 8-14 μm atmospheric window commonly referred to as long-wavelength IR (LWIR) detectors are a critical component in many of the military and civilian imaging systems. Since both quantum efficiency and detectivity depend upon the absorption and recombination lifetimes, an alternative to HgCdTe—like materials used in LWIR devices with stronger absorption coefficient and higher Auger recombination lifetimes is desirable as it allows the users to operate the device at higher temperatures.
Prior art teaches that a decrease in the band gap of Kane-like semiconductors generally yields to lower effective masses, hence affecting detrimentally both the absorption and Auger recombination coefficients.
It has been long known that small quantity of nitrogen in semiconductor materials like GaAs and GaP form a deep level impurity.1 More recently, the unusual large band gap lowering observed in (In)GaAs1-xNx with low nitrogen fraction2-6 has sparked a new interest in the development of dilute nitrogen containing III-V semiconductors for longwavelength optoelectronic devices such as near IR lasers, detector, and solar cells.3, 4-12 In spite of the decrease in the band gap, the conduction band effective mass has been predicted to rise with increasing nitrogen content, contrary to the expectation of usual k.p theory. The strong band gap bowing and increase in effective mass have been explained by a band anti-crossing model13 considering the interaction of the localized nitrogen states with the extended states of the conduction band. Within the context of Ga(In)AsN alloys, significant enhancements of electron effective masses have been evidenced experimentally and has been directly correlated to the increase in exciton binding energies5,6 and to the absorption strength in both bulk like and low dimensional heterosuctures.11,12,14,15 
As for LWIR applications, the alloying of nitrogen (N) with InSb, a direct band gap III-V semiconductor material with a room temperature band gap of 0.17 eV (7.4 μm), has been ventured by several groups. A significant reduction of the bandgap with increasing N concentration has been experimentally evidenced for InNxSb1-x alloys and semi-metallic behavior has recently been reported16 for alloys containing ˜6% of nitrogen.
Theoretically, a band gap closure (Eg=0) has been predicted for bulk-like InNxSb1-x containing x˜2% of nitrogen.17 Hence, dilute nitride InNxSb1-x can be used for the far infrared detection devices for the wavelength regime of 7 μm and beyond. Higher effective masses in the dilute nitride III-V materials are expected to curb the Auger recombination in the device, hence increasing the sensitivity of the material as a detector.17 Proper design of an infrared detector operating at a given temperature requires a detailed knowledge of the properties of the constituent semiconductor material.
The present invention described herein overcomes some well know barriers to existing materials used in infrared detection equipment by providing a method and process to design and fabricate improved long-wavelength infrared sensor materials. More specifically, the present invention discloses the use of dilute nitride alloys of InNxSb1-x under biaxial tensile stress (i.e. pseudomorpically strained to InSb (001)) to significantly enhance the detectivity and the operation temperature of LWIR devices and to extract precise compositions necessary to realize such improvement. It also teaches the fabrication of epitaxial films with a method for the synthesis of the alloys.